Help with adding avatar

Hi folks,
I wanted to add an avatar, but no matter how small I resize my picture, it won't get small enough to post. It stays above 15kb even when I have shrunk it so tiny it looks like a pinpoint...can't figure this one out. Any advice?

GIF = smaller file ... I'm not sure why exactly other than that it saves less information than a JPEG and therefore requires fewer bytes. I really should learn more about file formats since I have to use so many of them